20 CFR 228.15: Reduction for age.

(a) Widow(er), surviving divorced spouse, or remarried widow(er). The tier I annuity component is reduced 19/40 of 1 percent multiplied by the number of months before the annuitant attains full retirement age (presently age 65) effective with the annuity beginning date for widow(ers) born before 1/2/40. (For widow(ers) born after 1/1/40, see section 216(l) of the Social Security Act.)

(b) Disabled widow(er), disabled surviving divorced spouse, or disabled remarried widow(er). The tier I annuity component is reduced for a maximum of 60 months even though the annuity may begin at age 50.